NPR has a 24/7 streaming option from their "All Songs Considered" show. I've found it to be a great way to really discover music I probably wouldn't have ever heard of before otherwise. If a track comes along I dig, I'll see if the band is available on Spotify and if I like 60% of what I hear, I'll seek out the CD/Vinyl.

Recently I've been using Amazon MP3, but wondering if I should stop. The quality is fine, but wondering if I should just rip CD's myself. More Japanese bands are adding their music to Amazon, and this helps me a ton because ordering CD's from overseas is expensive. A Japanese CD is sometimes $25-40 after shipping yo.